WarmupAssign oxidation numbers to each

element:

Na NaCl Cl2H2O Ca(OH)2 NO3

-

ElectrochemistryElectrochemistry

is the basis for:is the basis for:

• Batteries and CorrosionBatteries and Corrosion• Industrial production of chemicalsIndustrial production of chemicals• Biological redox reactionsBiological redox reactions

The oxidation numbers of elements in their compoundsThe oxidation numbers of elements in their compounds

4.4

Reviewing Oxidation NumbersReviewing Oxidation Numbers

11

2

00

22

ClNaClNa

2

2

1

OH2(+1) + (-2) = 02(+1) + (-2) = 0 H O H O

2

122

)(

HOCa(+2) + 2(-2) + 2(+1) = 0(+2) + 2(-2) + 2(+1) = 0 Ca O H Ca O H

3

2?

ONX + 3(-2) = -1N O

X = +5X = +5

LEOLEO says says GERGER::

eNaNa10

LLose ose EElectrons = lectrons = OOxidationxidation

Sodium is oxidizedSodium is oxidized

GGain ain EElectrons = lectrons = RReductioneduction

10 CleCl Chlorine is reducedChlorine is reduced

11

2

00

22

ClNaClNa

Sr + 2HSr + 2H22O Sr(OH)O Sr(OH)22 + H + H22

TiClTiCl44 + 2Mg Ti + 2MgCl + 2Mg Ti + 2MgCl22

00 +1+1 +2+2 00

00+4+4 00 +2+2

Assign oxidation numbers to each Assign oxidation numbers to each species. Then identify the oxidizer species. Then identify the oxidizer

and reducer.and reducer.

But how do we know who will give electrons to who and if the reaction will be spontaneous?

Some reactions are spontaneous and can generate an electric current

Redox (oxidation-reduction) reactions involve the transfer of electrons

Some are nonspontaneous and can be caused by imposing an electric current (lab)

The Activity Series for Metals

LithiumLithium PotassiumPotassium CalciumCalcium SodiumSodium MagnesiuMagnesiumm AluminumAluminum ZincZinc ChromiumChromium IronIron NickelNickel LeadLead HydrogenHydrogen BismuthBismuth CopperCopper MercuryMercury SilverSilver PlatinumPlatinum GoldGold

Some standard Reduction Potentials at 25C E (volts)

F2(g) + 2e- 2F-(aq) +2.87

Au3+ + 3e- Au(s) +1.50Cl2(g) + 2e- 2Cl-(aq) +1.36

O2(g) + 4H3O+(aq) + 4e- 6H2O(l) +1.23

Br2(l) + 2e- 2Br-(aq) +1.08

Ag+(aq) + e- Ag(s) +0.80Hg2

2+(aq) + 2e- 2Hg(l) +0.79

I2(s) + 2e- 2I-(aq) +0.535

Cu2+(aq) + 2e- Cu(s) +0.337Sn4+(aq) + 2e- Sn2+(aq) +0.15Sn2+(aq) + 2e- Sn(s) -0.14Cd2+(aq) + 2e- Cd(s) -0.40Zn2+(aq) + 2e- Zn(s) -0.7632H2O(l) + 2e- H2(g) + 2OH-(aq) -0.828

Al3+(aq) + 3e- Al(s) -1.66K+(aq) + e- K(s) -2.93Li+(aq) + e- Li(s) -3.045

Using data from the previous reduction potential table, predict which of the following is the best oxidizerHint: good oxidizing agents are really good at stealing electrons and “getting reduced”a)F2 b) Ag+ c) Cd2+ d) Al3+

Using data from the previous reduction potential table, predict which of the following is the best reducing agent.Hint: good reducers are really good at donating electrons……and really bad at STEALING them.a) I2 b) Au3+ c) Br2 e) Sn2+

The Activity Series for Metals

LithiumLithium PotassiumPotassium CalciumCalcium SodiumSodium MagnesiuMagnesiumm AluminumAluminum ZincZinc ChromiumChromium IronIron NickelNickel LeadLead HydrogenHydrogen BismuthBismuth CopperCopper MercuryMercury SilverSilver PlatinumPlatinum GoldGold

Some standard Reduction Potentials at 25C E (volts)

F2(g) + 2e- 2F-(aq) +2.87

Au3+ + 3e- Au(s) +1.50Cl2(g) + 2e- 2Cl-(aq) +1.36

O2(g) + 4H3O+(aq) + 4e- 6H2O(l) +1.23

Br2(l) + 2e- 2Br-(aq) +1.08

Ag+(aq) + e- Ag(s) +0.80Hg2

2+(aq) + 2e- 2Hg(l) +0.79

I2(s) + 2e- 2I-(aq) +0.535

Cu2+(aq) + 2e- Cu(s) +0.337Sn4+(aq) + 2e- Sn2+(aq) +0.15Sn2+(aq) + 2e- Sn(s) -0.14Cd2+(aq) + 2e- Cd(s) -0.40Zn2+(aq) + 2e- Zn(s) -0.7632H2O(l) + 2e- H2(g) + 2OH-(aq) -0.828

Al3+(aq) + 3e- Al(s) -1.66K+(aq) + e- K(s) -2.93Li+(aq) + e- Li(s) -3.045

Calculate E° for a voltaic cell in which the reaction is:

2Ag+(aq) + Cd(s) 2Ag(s) +Cd2+(aq)

a) split into 2 half reactions

2Ag+(aq) + 2e- 2Ag(s)

Cd2+(aq) + 2e- Cd(s)

Cd(s) Cd2+(aq) + 2e-

b) Find E° values on table

Don’t multiply potential by # moles: electric potentials are ”intensive properties” and do not depend on the amount of the substance

Et° +0.80 + +0.40 = 1.20 V

The reaction will always happen in a way where the Et

is + (spontaneous)

E° = -0.40V

reversed, = + 0.40 V

E° = + 0.80V

Calculate ET° for the following reaction:2Al3+(aq) + 3Cd(s) 2Al(s) + 3Cd2+(aq)

a)-2.06 V b) -4.52 V c) +4.52 V

d) -1.26 V e) +2.06 V

Al3+(aq) + 3e- Al(s) E° = -1.66Cd2+(aq) + 2e- Cd(s E° = -0.40

E° = -1.66 + 0.40

Write the cell notation:

Zn|Zn2+||Cu2+|Cu

Which reaction

occurs at the anode?

Oxidation

Zn(s) Zn2+(aq) + 2e-

Which reaction occurs at

the cathode?

Reduction

Cu2+(aq) + 2e- Cu(s)

Voltaic Cellse- are produced at the anode and travel to the cathode. This causes ions to migrate to the electrodes and undergo redox reactions. After some time, the [ ] change.

salt bridge maintains electroneutrality and allows a current to flow. Otherwise, there would be a pile-up of electrons, and the current would stop. If there were no salt bridge, the reactants would simply mix together and react directly rather than sending electrons through a wire. Consequently, no current would flow, and there would not be a cell.

Reduction Potentials

Pb2+ + 2e¯ Pb -0.13 V

Al3+ + 3e¯ Al -1.68 V

Label the cathode and anode.

What voltage will be produced by the voltaic cell?

a) 2.97Vb) 1.55Vc) -1.81Vd) -2.97V

Cathode

(reduction, e- accepted here)

anode

(oxidation, e- given away here)